Field of the Invention
The present invention relates to an image capturing apparatus and an image capturing method.
Description of the Related Art
In recent years, various functions for assisting shooting in an image capturing apparatus, such as a digital video camera, have been proposed. For example, blur correction functions are installed in many image capturing apparatuses, and are classified into optical blur correction and electronic blur correction, depending on the correction method. The optical blur correction is a method in which a shake of an image capturing apparatus is detected, and a change of the optical axis due to the shake is cancelled by displacing a correction lens, which is part of an image capturing optical system, based on the detected shake. The electronic blur correction is a method in which a shake of an image capturing apparatus is detected using a motion vector in a captured image, and when an image for recording is generated using a captured image in an image memory, a position of the image memory from which the captured image is read out is changed so as to correct a shift between frames caused by the shake of the image capturing apparatus.
A function of performing object tracking using the correction lens used in the optical blur correction in order to include a moving object within a screen has also been proposed as a shooting assist function. Japanese Patent Laid-Open No. 2010-093362discloses a technique of using a blur correction lens to perform object tracking in order to include a main object within an angle of view until shooting is started, and switching control of the correction lens so as to use the blur correction lens to perform blur correction during shooting.
However, if the blur correction lens is moved with movement of the main object position, the position of an object (e.g., a still object such as one in the scenery) other than the main object within the screen changes, and accordingly this change is detected as a motion vector. If the electronic blur correction based on this motion vector is performed, the object tracking does not function correctly. The details will now be described, taking FIGS. 1A to 1E as an example.
FIG. 1A shows an image captured when the positional relationship between an image capturing apparatus and objects is in a state shown in FIG. 1B, and similarly, FIG. 1C shows an image captured when the positional relationship between an image capturing apparatus and objects is in a state shown in FIG. 1D. FIG. 1E shows a motion vector calculated from the images in FIGS. 1A and 1C. Note that regions divided in a lattice pattern within a motion vector detection area in FIG. 1A indicate blocks used in a later-described block matching method. A motion vector shown in FIG. 1E is a representative vector indicating movement of the entire screen calculated from motion vectors detected in the blocks.
As shown in FIG. 1A, a person, who is the main object in the captured image, is located at the center of the captured image. Here, if the person moves as shown in FIGS. 1B and 1D and the correction lens is driven so as to track the main object, the optical axis is inclined, and the person continues to be located at the center of the captured image as shown in FIG. 1C. In this case, the position of the scenery (building and tree in FIG. 1C) excluding the person in the captured image changes from the position in FIG. 1A to the position in FIG. 1C. Since the region other than the region of the person (blocks with a diagonal line in FIG. 1E) occupies large part of the captured image, the representative vector based on the change of the position in the background (scenery) is calculated as shown in FIG. 1E.
Here, as the electronic blur correction function, a method is widely used in which image blur is detected using a representative vector and the position of the image memory from which the captured image is read out is changed based on the representative vector. If this electronic blur correction function changes the position of the image memory from which the captured image is read out, based on the representative vector detected as a result of the background position changing when object tracking is performed using the correction lens as mentioned above, it may possibly interfere with the object tracking.